1. Field of the Invention
The present invention relates to the purification of exhaust gases emitted from, the improvement of an output of, and a reduction in the level of combustion noise generated in, a direct fuel injection internal combustion engine.
2. Description of the Related Art
In a direct fuel injection internal combustion engine, soot is produced in a combustion process particularly during medium- and high-load running, and this soot together with exhaust gases is emitted to the atmosphere and constitutes one of the causes of air pollution. To control the production of such soot, an internal combustion engine of this type (Japanese Utility Model Laid-Open No. 193123/1987) has hitherto been proposed in which an air jet is caused to collide against fuel or an air jet is injected into a combustion chamber during a latter stage of combustion. The internal combustion engine of the aforementioned type comprises an air chamber formed by an auxiliary cylinder and an auxiliary piston; an air injection passage communicating with the air chamber and a combustion chamber; an air intake passage communicating with the air chamber and the combustion chamber; and an auxiliary piston controlling means which is rotatively coupled with a crank and is adapted to move the auxiliary piston at a predetermined timing such that the communication between the air intake passage and the air chamber is canceled and the air inside the air chamber is compressed so as to inject air into the compression chamber. As such, the structure of the auxiliary piston controlling means is complicated, and, inevitably, an increase in the loss of driving power results and a head portion of the internal combustion engine becomes large in size. In addition, the combustion at its early stage is accompanied by a rapid pressure rise, as shown by the broken line in FIG. 2, constituting a cause of combustion noise, and high pressure and high temperature of the combustion chamber result in the emissions of NO.sub.x.
As another prior art, an arrangement is known which is aimed at obtaining a fixed compression pressure for an internal combustion engine (Japanese Patent Laid-Open No. 92424/1974). This arrangement is such that, in an extensive range of load fluctuations of the internal combustion engine, a pressure regulating piston during a low load is actuated and held in such a manner as to increase the compression pressure, and the pressure regulating piston during a high load is actuated and held in a position for lowering the compression pressure. Consequently, since, during the running of the engine when the load is fixed, the pressure regulating piston is fixed in a position determined by the combustion pressure by means of oil located in its rear so as not to move, it is impossible to obtain an effective emission of exhaust gases from a pressure adjusting chamber to the combustion chamber.